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Abstract:

The kinematic platform is a spherical-prismatic-spherical kinematic
platform providing six degrees of freedom with controlled braking at each
joint. The kinematic platform includes a base and an upper platform
plate, with the upper platform plate having opposed upper and lower
surfaces. The upper surface thereof provides a mounting surface for an
external article to which controlled three-dimensional movement is to be
imparted. A plurality of linear actuators are further provided, with each
linear actuator having opposed upper and lower ends. A plurality of upper
and lower spherical joints are provided for pivotally mounting the linear
actuators between the upper platform plate and a lower base. Each
spherical joint provides selective and controllable braking, allowing for
the controlled rotation of each end of each linear actuator with respect
to the respective upper platform plate or base.

Claims:

1. A kinematic platform, comprising: a base having opposed upper and
lower surfaces, the lower surface being adapted for mounting on a support
surface; an upper platform plate having opposed upper and lower surfaces;
a plurality of linear actuators, each of the linear actuators having
opposed upper and lower ends and a prismatic joint between the upper and
lower ends; means for selectively actuating each of the linear actuators;
a plurality of upper spherical joints pivotally connecting the upper ends
of the linear actuators to the lower surface of the upper platform plate;
a plurality of lower spherical joints pivotally connecting the lower ends
of the linear actuators to the upper surface of the base, each of the
upper and lower spherical joints having: a joint housing having an open
interior region and at least one open end; at least one electromagnet
disposed within the open interior region of the joint housing; a
spherical joint member positioned against the at least one electromagnet;
and at least one cover member securing at least a portion of the
spherical joint member within the joint housing so that the spherical
joint member frictionally engages the at least one electromagnet; and
means for selectively braking pivoting of the spherical joints; whereby
the at least one electromagnet may be braked to selectively control the
degree of magnetic attraction between the spherical joint member and the
electromagnet to selectively control rotational freedom of the spherical
joint member with respect to the at least one electromagnet and the joint
housing.

2. The kinematic platform as recited in claim 1, wherein each of said
upper and lower spherical joints further comprises a substantially
concave cup mounted on the at least one electromagnet for bearing against
a portion of the spherical joint member.

3. The kinematic platform as recited in claim 2, wherein each of said
upper and lower spherical joints further comprises at least one spring
mounted between the at least one electromagnet and a closed end of the
joint housing to spring-bias the at least one electromagnet against the
spherical joint member.

4. The kinematic platform as recited in claim 3, wherein each said
spherical joint member comprises: an outer spherical retaining shell
having an outer wall and an internal wall, the retaining shell defining
an aperture; at least one internal spherical sectioned member disposed
inside the outer retaining shell, the at least one sectioned member being
in contact with the internal wall of the outer retaining shell; an
actuator having at least one piston, the at least one piston being
secured to the at least one internal spherical sectioned member, the end
of the respective linear actuator being mounted to the actuator and
extending through the shell aperture; a third internal spherical
sectioned member attached to the actuator; and means for relaying braking
and release commands from a controller, the actuator responsively varying
friction between the at least one spherical section and the internal wall
of the spherical retaining shell, thereby selectively braking and
alternately allowing rotational motion of the at least one internal
spherical section and the elongate member relative to the outer spherical
retaining shell.

5. The kinematic platform as recited in claim 1, wherein the at least one
electromagnet of each of said upper and lower spherical joints has a
recess formed in one end thereof for receiving a portion of the spherical
joint member.

6. The kinematic platform as recited in claim 5, wherein each said
spherical joint member comprises: an outer spherical retaining shell
having an outer wall and an internal wall, the retaining shell defining
an aperture; at least one internal spherical sectioned member disposed
inside the outer retaining shell, the at least one sectioned member being
in contact with the internal wall of the outer retaining shell; an
actuator having at least one piston, the at least one piston being
secured to the at least one internal spherical sectioned member, the end
of the respective linear actuator being mounted to the actuator and
extending through the shell aperture; a third internal spherical
sectioned member attached to the actuator; and means for relaying braking
and release commands from a controller, the actuator responsively varying
friction between the at least one spherical section and the internal wall
of the spherical retaining shell, thereby selectively braking and
alternately allowing rotational motion of the at least one internal
spherical section and the elongate member relative to the outer spherical
retaining shell.

7. The kinematic platform as recited in claim 1, wherein the plurality of
linear actuators consists of three linear actuators.

8. The kinematic platform as recited in claim 1, wherein the pluralities
of upper and lower spherical joints respectively comprise at least three
upper spherical joints and at least three lower spherical joints.

9. A kinematic platform, comprising: a base having opposed upper and
lower surfaces, the lower surface being adapted for mounting on a support
surface; an upper platform plate having opposed upper and lower surfaces;
a plurality of linear actuators, each of the linear actuators having
opposed upper and lower ends and a prismatic joint between the upper and
lower ends; means for selectively actuating each of the linear actuators;
a plurality of upper spherical joints pivotally connecting the upper ends
of the linear actuators to the lower surface of the upper platform plate;
a plurality of lower spherical joints pivotally connecting the lower ends
of the linear actuators to the upper surface of the base, each of the
upper and lower spherical joints having: an outer spherical retaining
shell having an outer wall and an internal wall, the retaining shell
defining an aperture; at least one internal spherical sectioned member
disposed inside the outer retaining shell, the at least one sectioned
member being in contact with the internal wall of the outer retaining
shell; an actuator having at least one piston, the at least one piston
being secured to the at least one internal spherical sectioned member,
whereby the respective end of the respective linear actuator is mounted
to the actuator and extends through the shell aperture; and a third
internal spherical sectioned member attached to the actuator; and a
controller connected to the actuator for selectively controlling movement
of the actuator to vary friction between the at least one spherical
section and the internal wall of the spherical retaining shell, thereby
selectively braking and alternately allowing rotational motion of the at
least one internal spherical section and the elongate member relative to
the outer spherical retaining shell.

10. The kinematic platform as recited in claim 9, wherein each of said
upper and lower spherical joints further comprises: a joint housing
having an open interior region and at least one open end; at least one
electromagnet disposed within the open interior region of the joint
housing so that the outer spherical retaining shell is at least partially
disposed within the joint housing and is positioned against the at least
one electromagnet; and at least one cover member securing at least a
portion of the outer spherical retaining shell within the joint housing
so that the outer spherical retaining shell bears against the at least
one electromagnet, whereby the at least one electromagnet may be actuated
to selectively control the degree of magnetic attraction therebetween to
selectively control rotational freedom of the outer spherical retaining
shell with respect to the at least one electromagnet and the joint
housing.

11. The kinematic platform as recited in claim 10, wherein each of said
upper and lower spherical joints further comprises a substantially
concave cup mounted on the at least one electromagnet for receiving a
portion of the outer spherical retaining shell.

12. The kinematic platform as recited in claim 11, wherein each of said
upper and lower spherical joints further comprises at least one spring
mounted between the at least one electromagnet and a closed end of the
joint housing to spring-bias the at least one electromagnet against the
outer spherical retaining shell.

13. The kinematic platform as recited in claim 12, wherein the at least
one electromagnet of each of said upper and lower spherical joints has a
recess formed in one end thereof for receiving a portion of the outer
spherical retaining shell.

14. The kinematic platform as recited in claim 9, wherein each of said
upper and lower spherical joints further comprises: a joint housing
having an open interior region and at least one open end, the outer
spherical retaining shell being disposed therein; a plurality of
frictionally engaging members received within the joint housing so that
the outer spherical retaining shell is substantially centrally positioned
therein, the outer wall thereof contacting the plurality of frictionally
engaging members; and at least one cover member securing at least a
portion of the outer spherical retaining shell within the joint housing
such that the outer spherical retaining shell frictionally engages the
plurality of frictionally engaging members.

15. The kinematic platform as recited in claim 14, wherein the plurality
of frictionally engaging members comprise a plurality of ball bearings.

16. The kinematic platform as recited in claim 9, wherein the plurality
of linear actuators consists of three linear actuators.

17. The kinematic platform as recited in claim 9, wherein the pluralities
of upper and lower spherical joints respectively comprise at least three
upper spherical joints and at least three lower spherical joints.

18. A kinematic platform, comprising: a base having opposed upper and
lower surfaces, the lower surface being adapted for mounting on a support
surface; an upper platform plate having opposed upper and lower surfaces;
three prismatic actuators, each of the prismatic actuators having opposed
upper and lower ends and a prismatic joint between the upper and lower
ends; means for selectively actuating each of the prismatic actuators;
three upper spherical joints pivotally connecting the upper ends of the
linear actuators to the lower surface of the upper platform plate; three
lower spherical joints pivotally connecting the lower ends of the linear
actuators to the upper surface of the base, each of the upper and lower
spherical joints having: a joint housing having an open interior region
and at least one open end; at least one electromagnet disposed within the
open interior region of the joint housing; a spherical joint member
positioned against the at least one electromagnet; and at least one cover
member securing at least a portion of the spherical joint member within
the joint housing so that the spherical joint member bears against the at
least one electromagnet; and a controller connected to the at least one
electromagnet and operable to selectively control the degree of magnetic
attraction therebetween to selectively control rotational freedom of the
spherical joint member with respect to the at least one electromagnet and
the joint housing.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to movable or adjustable platforms
and to tripods, and particularly to a kinematic platform having three
spherical-prismatic-spherical legs providing six degrees of freedom with
controlled braking at each joint and high dexterity within the workspace.

[0003] 2. Description of the Related Art

[0004] A need exists for simple and effective parallel kinematics
mechanisms. Kinematics mechanisms are used in mechanical engineering
applications for machining, robotics, positioning devices, coordinate
measuring, fixtures, etc. Serial kinematics mechanisms are widely used
and presently dominate the market. A serial kinematics mechanism has a
series of cantilever beams that are movably connected together in an
end-to-end fashion by prismatic, revolute or spherical joints, forming an
open loop. The closer that a member is to a base of the mechanism within
the serial structure, the higher the load on that member. Additionally,
the farther that a member is from the base, the higher its deflection
with respect to the base member. When a serial kinematics mechanism is
subjected to loading, the position of the farthest member; i.e., the
end-effector, is subject to the cumulative deflections of all serial
members. Unfortunately, this results in large positioning errors at the
end-effector. Being constructed of cantilevers, a serial mechanism has a
poor stiffness to mass ratio, making such structures bulky in design with
difficult in control of the joints.

[0005] Serial kinematics mechanisms allow fast and easy computation of the
position of the end-effector given the position or state of all
actuators. In general, this computation is known as the forward
kinematics of a mechanism. However, determining the position or state of
all actuators given the position of the end-effector, also known as the
inverse kinematics, is very difficult. Particularly, control over
rotation of the joints is of primary concern in serial kinematic
platforms.

[0006] Numerous ball and socket joints having manual joint locking
mechanisms exist. Such mechanisms are usually very complex and due to the
manual locking are not suitable for robotic or parallel kinematic machine
operations. Even lockable joint devices linked to hydraulic systems may
not be suitable for robotic applications, or the like. Moreover, ball
joints with detent stopping action do not lock to an arbitrarily desired
position, and therefore are not precise enough for robotic machine
applications. It would be very desirable to overcome the aforementioned
problems caused by the use of existing ball joint mechanisms. Thus, a
kinematic platform solving the aforementioned problems is desired.

SUMMARY OF THE INVENTION

[0007] The kinematic platform is a spherical-prismatic-spherical kinematic
platform providing six degrees of freedom with controlled braking at each
joint. The kinematic platform includes a base having opposed upper and
lower surfaces, the lower surface being adapted for mounting on a support
surface, such as a table or the like. An upper platform plate is
provided, the upper platform plate having opposed upper and lower
surfaces. The upper surface of the platform provides a mounting surface
for an external article to which controlled three-dimensional movement is
to be imparted.

[0008] A plurality of linear actuators are further provided, with each
linear actuator having opposed upper and lower ends. Preferably, at least
three such linear actuators are provided and, in the preferred
embodiment, the linear actuators are prismatic actuators that may be
selectively actuated by an external controller. A plurality of upper
spherical joints are respectively mounted to the lower surface of the
upper platform plate so that the upper ends of the plurality of linear
actuators are pivotally mounted to the upper platform plate. Similarly, a
plurality of lower spherical joints are respectively mounted to the upper
surface of the base so that the lower ends of the plurality of linear
actuators are pivotally mounted to the base.

[0009] In one embodiment, each of the upper and lower spherical joints
includes a joint housing having an open interior region and at least one
open end for receiving at least one electromagnet. A spherical joint
member formed from a ferromagnetic or paramagnetic material is positioned
against the at least one electromagnet, and at least one cover member
secures at least a portion of the spherical joint member within the joint
housing so that the spherical joint member frictionally engages the at
least one electromagnet. In use, the at least one electromagnet may be
selectively and controllably actuated by the external controller to
selectively control the degree of frictional engagement between the
spherical joint member and the electromagnet to selectively control
rotational freedom of the spherical joint member with respect to the at
least one electromagnet and the joint housing.

[0010] These and other features of the present invention will become
readily apparent upon further review of the following specification and
drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a perspective view of a kinematic platform according to
the present invention.

[0012] FIG. 2 is a partial perspective view of one leg of the kinematic
platform according to the present invention, showing details of a
spherical joint attaching the leg to the base.

[0013] FIG. 3 is an exploded perspective view of a spherical joint of the
kinematic platform according to the present invention.

[0014] FIG. 4 is a side view in section of an alternative embodiment of a
spherical joint for a kinematic platform according to the present
invention.

[0015] FIG. 5 is a side view in section of another alternative embodiment
of a spherical joint for a kinematic platform according to the present
invention.

[0016] FIG. 6 is a side view in section of another alternative embodiment
of a spherical joint for a kinematic platform according to the present
invention.

[0017] FIG. 7 is a side view in section of a further alternative
embodiment of a spherical joint for a kinematic platform according to the
present invention.

[0018] FIG. 8 is a side view in section of another alternative embodiment
of a spherical joint for a kinematic platform according to the present
invention.

[0019] FIG. 9 is a side view of yet another alternative embodiment of a
spherical joint for a kinematic platform according to the present
invention.

[0020] Similar reference characters denote corresponding features
consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] As best shown in FIG. 1, the kinematic platform 10 is a
spherical-prismatic-spherical kinematic platform providing six degrees of
freedom with controlled braking at each joint. The kinematic platform 10
includes a base 12 having opposed upper and lower surfaces, the lower
surface being adapted for mounting on a support surface, such as a table
or the like. An upper platform plate 14 is further provided, with the
upper platform plate 14 having opposed upper and lower surfaces. The
upper surface of the platform 14 provides a mounting surface for an
external article to which controlled three-dimensional movement is to be
imparted.

[0022] A plurality of linear actuators 18 (spherical-prismatic-spherical
legs, which may be actuated electrically, pneumatically, hydraulically,
etc.) are further provided, each linear actuator 18 having opposed upper
and lower ends. Preferably, at least three such linear actuators 18 are
provided, and, in the preferred embodiment, the linear actuators 18 are
prismatic actuators that may be selectively actuated by an external
controller 16. It should be understood that any suitable type of linear
actuator may be utilized. Similarly, it should be understood that any
suitable number of linear actuators 18 may be used. Although three such
actuators 18 are shown in FIG. 1, it should be understood that the three
actuators 18 are illustrated for exemplary purposes only. The controller
16 may be any suitable type of controller, such as a programmable logic
controller, a proportional-integral-derivative (PID) controller, a
computer or the like.

[0023] A plurality of upper spherical joints 20 are respectively mounted
to the lower surface of the upper platform plate 14 so that the upper
ends of the plurality of linear actuators 18 are pivotally mounted to the
upper platform plate 14. As best shown in FIG. 2, a plurality of lower
spherical joints 21 are similarly mounted to the upper surface of the
base 12 so that the lower ends of the plurality of linear actuators 18
are pivotally mounted to the base 12.

[0024] The spherical joints have controllable braking to precisely
position the platform 14 in the desired orientation. In a first
embodiment, as illustrated in FIG. 3, each of the upper and lower
spherical joints includes a joint housing 20 having an open interior
region and at least one open end for receiving at least one electromagnet
24. It should be understood that any suitable type of electromagnet may
be utilized. The electromagnet 24 is controlled and actuated by the
external controller 16, which may be used to turn the electromagnet on
and off, or to control the strength of magnetic attraction between the
sphere and the electromagnet. Similarly, although a single electromagnet
24 is shown in FIG. 3, it should be understood that any desired number of
electromagnets may be received within the housing 20.

[0025] A spherical joint member 22 formed from a ferromagnetic or
paramagnetic material is positioned against the at least one
electromagnet 24, and at least one cover member 26 secures at least a
portion of the spherical joint member 22 within the joint housing 20 so
that the spherical joint member 22 frictionally engages the at least one
electromagnet 24. The cover member 26 may be secured to the open end of
housing 20 by any suitable type of bolts 30, screws, pins or the like,
which pass through apertures formed through the cover member 26.
Preferably, the electromagnet 24 is of the coil type, the core having an
open central passage 32 formed therethrough. The spherical joint member
22 is partially received within one open end of the central passage 32.

[0026] In use, the at least one electromagnet 24 may be selectively and
controllably actuated by the external controller 16 to selectively
control the degree of magnetic attraction between the spherical joint
member 22 and the electromagnet 24 to selectively control rotational
freedom of the spherical joint member 22 with respect to the at least one
electromagnet 24 and the joint housing 20. Thus, through selective
actuation of the linear actuators 18, the platform 14 is free to rotate
with six degrees of freedom, the individual spherical joints 20, 21
having controllable braking. A portion of the spherical joint member 22
projects through a central aperture 28 formed through the cover member 26
(as shown in FIG. 2), one end of a respective linear actuator 18 being
mounted to the sphere 22.

[0027] In the alternative embodiment illustrated in FIG. 4, a cup 36 is
mounted on the upper end of the electromagnet 24 for securely receiving a
lower portion of the spherical joint member 22, thereby increasing
surface contact between the sphere 22 and the electromagnet 24. Further,
in the embodiment of FIG. 4, the single cover 26 of FIG. 3 is replaced by
dual cover members 26a, 26b. It should be understood that any desired
number of cover members may be used to securely position the spherical
joint member 22 within the housing 20 and against the electromagnet 24.
Further, at least one resilient member, such as springs 34, is positioned
opposite the spherical joint member 22 to resiliently bias the
electromagnet 24 against the spherical joint member 22.

[0028] Alternatively, as shown in FIG. 5, the cup 36 may be removed and a
recess 38 may be formed in the proximal end of the electromagnet 24 for
directly receiving the lower end of the spherical joint member 22. In
FIGS. 4 and 5, firm contact between the cup 36 and the upper end of the
electromagnet 24, or the recess 38, with the lower end of the spherical
joint member 22 is desired, as the magnetic attraction therebetween
(along with the frictional engagement between the spherical member 22 and
the border defining aperture 28 of cover member 26) acts to selectively
and controllably brake rotation of the spherical joint member 22 with
respect to the housing 20. The frictional force is proportional to the
force acting normal on the spherical joint member (i.e., the magnetic
attraction between the electromagnet 24 and the spherical joint member
22), so controlling the magnitude of the magnetic force directly controls
the frictional force therebetween.

[0029] In the alternative embodiment of FIG. 6, the spherical joints 20,
21 are replaced by a spherical joint 40 that may be mounted directly to
the upper platform plate 14 or the base 12. The joint 40 includes an
outer retainer shell 42, and provides relative spherical motion between
the outer shell 42 and interior components 46 and 44. The spherical
motion is limited by the size of the aperture 49 formed in the spherical
shell 42, the maximum range of motion being achieved when the aperture
size is equal to the circumference of the external spherical shell 42.

[0030] The internal portion of the spherical joint 40 includes peripheral
spherical sections 44, which sandwich the central spherical section 46 to
form an internal sphere inside of outer spherical shell 42 and in close
proximity to an internal wall thereof. A solenoid, a piezoelectric
actuator, an electromagnetic actuator 48 or the like is further provided,
the actuator 48 having at least one piston 47 held by the central
spherical section 46. In FIG. 6, a pair of pistons 47 are shown for
pressing members 44 against the inner surface of shell 42, as will be
described in detail below, although it should be understood that one of
the members 44 may be fixed with respect to the shell 42 so that only a
single piston 47 and a single movable member 44 may be used as an
alternative. In the dual-piston arrangement of FIG. 6, the dual piston 47
has ends that are attached to the peripheral spherical sections 44.

[0031] Responsive to control signals received via a control line 19, which
extends through a hollow portion of the linear actuator 18 (the adjacent
end of which extends within the shell 42 through the aperture 49 and is
mounted to the actuator 48), the actuator 48 causes outward radial
mechanical displacement of the at least one piston 47. The mechanical
displacement applies an outward radial force that pushes the peripheral
sections 44 into frictional contact with the inner wall of the outer
spherical shell 42, thereby braking rotational motion of the linear
actuator 18. Braking and release control commands are delivered via the
control line 19 from the controller 16.

[0032] FIG. 7 illustrates an alternative embodiment in which the spherical
joint 40 is used in place of spherical joint member 20 in the embodiment
of FIG. 3. Thus, frictional engagement between the electromagnet 24 and
the shell 42 of joint 40 may be used in combination with the internal
braking of the movable piston of spherical joint 40, providing two
separate controllable braking mechanisms. Similarly, as shown in FIG. 8,
the spherical joint 40 may be used in combination with the embodiment of
FIG. 5, the shell 42 rotating in the recess 38.

[0033] In the further alternative embodiment of FIG. 9, the spherical
joint member 40 is received within a housing 20, similar to those of
FIGS. 7 and 8, but without an additional electromagnet 24. Instead, the
remainder of the housing 20 is filled with frictionally engaging members,
such as ball bearings 50, thus providing additional frictional engagement
to the internal braking of the spherical joint member 40.

[0034] It is to be understood that the present invention is not limited to
the embodiments described above, but encompasses any and all embodiments
within the scope of the following claims.